Negative Fuel Trims- 2.0L Z3- Lets test the MAF.

NZ00Z3

Zorg Guru (III)
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New Zealand Zeds
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Dec 9, 2014
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903
Location
Timaru, New Zealand
Model of Z
3.0L, 2.0L Z3 Roadsters
Hi

My 2.0L Z3 with a M52TUB20 engine has had negative long term fuel trims since I got it at about 92,000 miles. Now done around 30,000 miles in it. The trims haven't changed much, no codes and no problems. The LTFT1 is -5.5% and the LTFT2 is -6.3%. Its less than the usual >+/-8% and you have problems criteria.

Been doing a little research into it and one cause could be an over reporting MAF. A good Siemens/VDO MAF is not cheap and the after market ones don't have a good reputation. So, before spending my hard earnt cash, I decided to find out how to test a MAF.

The word is that if you plot Rev's against MAF flow in a graph/chart, it should be a straight line. If it shows an over reporting MAF then you have the cause of the negative fuel trims. Time to collect some data.

With the Foxwell NT530 in hand. Connected to the car in OBD2 mode (not BMW mode) as this is where I found the Rev's and MAF live data. Sat in the car and rev'ed it up in stages and manually recorded the Rev's and MAF values on paper. This was difficult as the rev's would change slightly and the MAF would follow with a change. A little bit of guess work and approximation was used in the end. Not a over reporting MAF, more of an under reporting MAF that would cause lean conditions.

Regards

Murray
 
Last edited:

Mint

Zorg Expert (I)
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British Zeds
East Anglian Crew
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Sep 23, 2012
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Stafford, UK
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2.2 & 3.0 Sport
Great research Murray:thumbsup:, hope the new MAF shows a different result.
 
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